Preparing nickel ferrite single crystals on a monocrystalline substrate



July 25, 1967 Filed June 21, 1962 MAGNETIC VALVE 12 MAGNETIC VALVE C.KOOY PREPARING NICKEL FERRITE SINGLE CRYSTALS 0N A MONOCRYSTALLINESUBSTRATE 3 She rats-Sheet l NICO B0 CO2 FB O27 MONOCRYSTAL FIG.1

FURNACE INVENTOR GORNELIS KOOY BY i i L I. AG T July 25, 1967 Y c. KOOY3,332,796

PREPARING NICKEL FERRITE SINGLE CRYSTALS ON A MONOCRYSTALLINE SUBSTRATEFiled June 21, 1962 3 Sheets-Sheet 2 FIG 2 28 2s 21. 22 2'0 fa 1 6 121'2 1qNVE-|TOR M0 CORNELIS KOOY BY 2 g AGEN July 25, 1967 C. KOOY3,332,796

PREPARING NICKEL FERRITE SINGLE CRYSTALS ON A MONOCRYSTALLINB SUBSTRATEFiled June 21, 1962 3 Sheets-Sheet 3 29 --Mo m FIGA 2e 2e 22. 22 2 0 fa1s 1:. 1'2 1 0 :1

INVENTOR GORNELIS KOOY BY AGENT United States Patent 6 3 Claims. (Cl.117-21) The invention relates to a method of manufacturing a singlecrystal body of a compound which is capable of being sintered.

It is known to manufacture single crystal bodies by melting the relativecompound and, during cooling, taking such measures that the particles ofthe solidifying melt arrange in a particular manner with respect to eachother. This may occur, for example, by inducing the crystallization inthe melt with a cold finger which usually comprises a small seedcrystal. It is also known to heat the powder of the compound in questionin the flame of an oxyhydrogen blowpipe, the powder being taken along bythe inner pipe of the .blowpipe. The powder is caught on a refractoryrod and solidifies to form a single crystal body. In these cases, themethod is carried out at the melt- .ing temperature of the purecompound. Naturally, the gas atmosphere should be adapted to theequilibrium of the compound at this temperature. In connection with thehigh melting temperature, this is often hard to realize, as a result ofwhich some compounds decompose entirely at the melting temperature.

Alternatively, methods are known which are carried out at a temperaturelower than the melting temperature of the pure compound. The meltcontains, in addition to the pure compound, one or more other compoundswhich are active as fluxes. This method may be used in those cases inwhich a suitable flux exists for the compound in question. In addition,special measures should be taken to influence the nucleation and tocheck uncontrolled nucleation.

The invention relates to a particular method which is also carried outbelow the melting temperature of the pure compound. It is based on therecognition of the fact that a controlled recrystallization takes placeif a thin layer of powdered particles is applied on a monocrystallinesubstratum and sintered.

In the method according to the invention, a layer of at most 2-00microns, preferably at most 20 microns, of a powder of the compound inquestion or of substances which form the compound in question on heatinghaving a particle size of at most microns, is provided on a singlecrystal body and heated to a temperature which lies in therecrystallization temperature range of the compound in question. Themethod is carried out below the melting temperature since therecrystallization temperature range lies below the melting temperature.The recrystallization temperature range lies between /2 and /3 of theabsolute melting temperature. A temperature in this range is sometimestermed Tamman temperature. With this method, the particles of the powderrecrystallize according to an ordered pattern as a result of themonocrystalline substrate on which it is provided. The thickness of thelayer is at most 200 microns to prevent arbitrary recrystallization fromtaking place in part of the applied layer. Good results are obtainedwith a layer thickness of at most 20 microns. The particles of thepowder are on the substrate in an arbitrary orientation. The orderedgrowth turns out to start from those particles of the powder which, asfar as the crystal orientation is concerned, are rationally linked withthose of the substrate. The particle size of the powder should be atmost 5 microns for the powder to be reactive.

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So the compound is not applied in an atomic or molecular form but in theform of small crystalline powdered particles. The powder may consist ofparticles of the compound in question. Then the method according to theinvention substantially comes to a recrystallization with a controllednucleation of the recrystallization nuclei. The powder may also consistof substances which form the compound in question on heating. In thiscase, both a reaction and an ordered crystallization take place. Thepowder is applied on a single crystal body. The composition of this bodymay be equal to that of the body to be manufactured but it may also havea different composition and even a crystal structure which differs fromthat of the single crystal body to be manufactured. In this latter case,a sufliciently large difference should exist between the interfacialsurface energy with respect to the substrate with oriented andnon-oriented particles of the powder so as to form recrystallizedorientation nuclei. The powder layer may be provided on the substrate invarious manners. It may be effected in the form of a suspension, afterwhich the substrate with the suspension layer are heated. It is alsopossible to provide a thin powder layer immediately on a heatedsubstrate by blowing the powder on it by means of a gas stream.

In this manner, thin monocrystalline layers are formed which can easilybe separated from the substrate. To obtain single crystal bodies havinga larger thickness, the method according to the invention is repeatedseveral times.

Compounds, of which single crystal bodies can be manufactured by meansof the method according to the invention are, for example, BaTiO andNiFe O Since it is very difficult to obtain a single crystal body ofNiFe Q, according to a known method, use is made according to theinvention of a signal crystal body having a magnetoplumbite structure,for example a body of a composition BaFe O or a single crystal bodyhaving a different hexagonal crystal structure, for example a body of acomposition BaCo Fe O In order that the invention may readily be carriedinto effect, it will now be described, by way of example, with referenceto the accompanying drawings and the ensuing examples.

FIG. 1 diagrammatically shows an apparatus which may be used in themethod according to the invention.

FIGS. 2, 3 and 4 show intensities of an X-ray diffraction pattern ofbodies manufactured according to the method according to the invention.

FIG. 5 shows the intensities of an X-ray diffraction pattern of a knownbody.

EXAMPLE I A mixture of NiCO and Fe O in a ratio of 1:1 was ground for 16hours in ethyl alcohol in a ball mill and then another 16 hours in avibrating mill. After drying, a suspension in amyl acetate withapproximately 0.25% nitrocellulose was made of the powder. Of thissuspension a 20 micron thick layer was coated on the (0001) face of asingle crystal body of SrFe O which, after drying, yielded ahomogeneously distributed layer of powder particles on the surface ofthe single crystal body. This was heated in oxygen for 15 minutes at 0C. Of this product an X-ray diffraction pattern was made which, inaddition to the reflections of the basal plane of the SrFe O singlecrystal, also showned the (111), (222), (333) and so on reflections ofthe spinel lattice of NiFeO The method was repeated several times. Afterfive times, the X-ray diffraction diagram invariably showed only the(111) reflections of spinel and those of the basal plane of SrFe O fromwhich it appears that the layer of NiFe O formed is monocrystalline orthat it has a very pronounced orientation with the (111)-axis parallelto the hexagonal c-axis of the substrate crystal.

EXAMPLE II By means of the apparatus diagrammatically shown in FIGURE 1,small portions of a powdered mixture of NiCO and Fe O in a ratio of 1:1where applied on the (0001) face of a single crystal body of Baco Fe Owhich was at a temperature of 1325 C. The tube furnace 1 contains thesaid single crystal body 2. On the one side, the aluminum oxide tube 3extends in the furnace so that it nearly touches the single crystal body2. By means of a connecting limb 4 the tube 3 is connected to the glasstube 5 having two branches. The glass container 6 containing the powdermixture 7 of NiCO and Fe O is provided in the one branch. The tube 8which comprises a magnetic shutter 9 and a flow meter 10 extends in thevessel 6 in the powder mixture 7. The other branch of the tube 5comprises a magnetic shutter 11 and a flow meter 12. A stream of oxygenwas blown through the tube 8 at a rate of from 5 to 10 liters/ min.which caused eddies in the container 6, as a result of which the powderwas more or less fluidized and the smallest particles were conductedinto the tube 5 over such a distance that they Were blown on the singlecrystal body 2 at a rate of from 10 to 15 liters/min. by a stream ofoxygen supplied to the other branch of the tube 5. The furnacetemperature was 1325 C. By controlling the magnetic shutters, powder wasblown on the single crystal body for 2 seconds every 10 minutes. 0.2 to0.4 mg. of the powder mixture were applied to the surface of the singlecrystal body which had an area of 0.5 x 0.5 cm. This method was repeatedmany times. The results are shown in FIGURES 2, 3 and 4 which are X-raydiffraction patterns after 14, 68 and 106 operations respectively. Inthe figures the intensity I of the reflections of a MoKa radiation isplotted in an arbitrary unit as a function of a deflection angle 20.From the increase of the ratio of the intensities of the (111) spinelreflection and the basal reflections of BaCo Fe O it may be concludedthat an ordered spinel layer is formed on the single crystal substrate.The orientation follows from the absence of all reflections other thanthose of the (111) plane. In FIGURE 4, the peak of the (333) line fallsoutside the plane of the drawing. For comparison, FIGURE 5 shows thereflections of a body constituting of NiFe O in which the particles arearbitrarily present. Single crystal bodies obtained in this manner andhaving thicknesses of from 100 to 300 microns could be detached from thesubstrate.

The same result was obtained in a method in which the mixture of NiCOand Fe O was replaced by a powder of NiFe O which was obtained byheating the powder mixture of NiCO and Fe O at 1000 C. and grinding thereaction product in alcohol in a ball mill for 16 hours and in avibrating mill for 8 hours and then drying it. I

\rVhat is claimed is:

1. A method of manufacturing a single crystal body of NiFe O comprisingthe steps of applying a layer of powder NiFe O not exeeding 2:00p. inthickness and composed of particles not exceeding 5 in diameter on amonocrystalline substrate of BaFe O and heating said layer to atemperature between /2 and /3 the absolute melting temperature of NiFe Oto thereby recrystallize the particles into a monocrystalline layer.

2. A method of manufacturing a single crystal body of NiFe O comprisingthe steps, applying a layer of NiFe O powder not exceeding 200p. inthickness and composed of particles not exceeding 5 in thickness on amonocrystalline substrate of BaCo Fe O and heating said layer to atemperature between /2 and /3 the absolute melting temperature of NiFeOg to thereby recrystallize the the particles into a monocrystallinebody.

3. A method of manufacturing a single crystal body of NiFe O comprisingthe steps, applying a layer of NiFe O powder not exceeding 200 inthickness and composed of particles each having a diameter not exceeding5 1 on a monocrystalline substrate of SrFe O and heating said layer to atemperature between /2 and /3 the absolute melting temperature of NiFe Oto thereby recrystallize the particles into a monocrystalline body.

References Cited UNITED STATES PATENTS 2,832,705 4/1958 Seidl 117168 X3,037,180 5/1962 Linz 25262.3 X 3,047,429 7/1962 Stoller 1172153,093,517 6/ 1963 Lyons 25262.3 X 3,100,158 8/1963 Lemaire 1172153,108,072 10/1963 Gutsche 252-62.3 X 3,109,749 11/1963 Di Ricco 1172l5NORMAN YUDKOFF, Primary Examiner.

MAURICE A. BRINDISI, Examiner.

H. T. CARTER, S. J. EMERY, Assistant Examiners.

1. A METHOD OF MANUFACTURING A SINGLE CRYSTAL BODY OF NIFE2O4 COMPRISINGTHE STEPS OF APPLYING A LAYER OF POWDER NIFE2O4 NOT EXCEEDING 200U INTHICKNESS AND COMPOSED OF PARTICLES NOT EXCEEDING 5U IN DIAMETER ON AMONOCRYSTALLINE SUBSTRATE OF BAFE12O19, AND HEATING SAID LAYER TO ATEMPERATURE BETWEEN 1/2 AND 2/3 THE ABSOLUTE MELTING TEMPERATURE OFNIFE2O4 TO THEREBY RECRYSTALLIZE THE PARTICLES INTO A MONOCRYSTALLINELAYER.